A Hall sensor is often used in magnetic applications to measure magnetic fields, or inspect materials. A Hall sensor includes a Hall plate, which is a semiconductor crystal that varies its voltage in response to a magnetic field. Hall effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications. Hall sensors are commonly used to time the speed of wheels and shafts, such as for internal combustion engine ignition timing, tachometers and anti-lock braking systems. They are used in brushless DC electric motors to detect the position of the permanent magnet. This arrangement can also be used to regulate the speed of disk drives.
Because Hall voltage is often on the order of millivolts, the output from this type of sensor cannot be used to directly drive actuators but instead must be amplified. In such amplifiers, offset voltages are often unavoidable. A chopper amplifier uses clock signals to control amplification of an input signals. It can reduce effect of offset voltage on signal amplification. Therefore chopper-controlled amplifiers have been used in the detection of Hall voltage.
Even though conventional chopper amplifiers have been used to reduce offset voltages in Hall voltage measurement, they are often not adequate in applications that require lower offset voltage. Therefore, improved techniques for more effective Hall voltage measurement with lower offset voltages are highly desirable.